The paint and coatings industry is faced with a number of challenges in developing suitable coating compositions that meet both governmental regulations and consumer preferences. One of these challenges is to satisfy the consumer's desire for improved appearance of the coating compositions, particularly with respect to effect coatings. Typically, aluminum flakes are used as pigments to give paint a metallic effect, although pearlescent mica flakes are also used. These flakes have a larger diameter compared to their thickness and typically should lay flat against each other to provide a brilliant appearance. Disorientation of the flakes causes light scatter, resulting in a dark and/or speckled appearance. Disorientation of the flakes can lead to irregular areas of lightness variation in total color impression. This is more obvious for light metallic colors on large body panels. In the coatings industry, this undesired appearance is called mottling.
The flake orientation is influenced by application parameters and rheology properties of the basecoat itself. A skilled sprayer can control flake orientation by changing atomizing air pressure, changing the size of a paint gun nozzle, changing the spraying distance from a substrate, and the like. Coating compositions with good flake control capability, i.e., suitable rheology and viscosity properties, are desirable so that a paint sprayer can easily apply the coating composition without the need to adjust flake orientation.
Another challenge is in the area of environmental regulations. Environmental concerns have resulted in government restrictions of volatile organic compounds (VOCs) in paints and coatings. For example, in the United States, many states have passed or are considering passing legislation limiting VOCs in refinish basecoats to no more than 0.42 kilograms (kg) of VOCs/liter of paint (3.5 pounds of VOCs/gallon of paint). Other countries have or will follow suit. Compliance with these regulations is currently possible by using “exempt” solvents, which are solvents that are not included in the calculation of VOCs. VOC exempt solvents do not cause the formation of ground level ozone (smog), according to environmental chemists. Several of the more commercially useful VOC exempt solvents include acetone, methyl acetate, tertiary butyl acetate (TBAc), and P-chlorobenzotriflouride (PCBTF). Water also is considered an exempt solvent.
For low solids coating compositions, significant amounts of exempt solvents are needed to achieve certain VOC targets. Due to the limitation of choice of solvents and the amount of non-exempt, but preferred, solvents, it becomes more challenging to formulate a coating composition that has both low VOC and that provides suitable rheology and viscosity for good effect color appearance.
Accordingly, it is desirable to provide low solids coating compositions with polyurea rheology control agents that improve the appearance, particularly the orientation of effect pigments, of the coating compositions. In addition, it is desirable to provide methods and systems for making such low solids coating compositions. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.